The “induction motor” is a common type of motor, which gets no electrical winding in its rotor assembly, and only its stator gets electrical winding.
Textbook definition of “nonmagnetic material”: materials whose permeabilities are the same as that for free space. (Examples of nonmagnetic materials include copper, and aluminum)
Textbook definition of “diamagnetic material”: materials that have permeabilities slightly less than that of free space.
There are three categories of systems used in refrigeration & a/c (air condition) system: the first is hermetic system in FIG. 1 (shown with a reciprocating compressor), the second is semi hermetic (also FIG. 1), the third is open type system in FIG. 2 (shown with a reciprocating compressor).
The open type system usually handles bigger capacity than the former two systems. In the open type system, the motor is not sealed with compressor in a dome and the leak from the compressor crankshaft seal is a constant problem (FIG. 2).
In a hermetic system (including a semi hermetic system), the whole motor and compressor are sealed with refrigerant in a dome (shell), the electrical entrance in the dome is a possible refrigerant leaking spot. In this system, the spark, fire and red hot winding caused by electric short circuit of the motor electric winding are major concerns. Because the electrical winding short circuit can generate heat which can burn the motor and the. This causes environment pollution (the destroyed refrigerant must be processed and dumped) and it is expensive to repair the motor. Also a hermetic system is typically not built to handle a large capacity, because of the potential difficulties in sealing a high power motor winding with refrigerant in a dome (shell).